List of animals displaying homosexual behavior

For these animals, there is documented evidence of homosexual behavior of one or more of the following kinds: sex, courtship, affection, pair bonding, or parenting, as noted in researcher and author Bruce Bagemihl's 1999 book Biological Exuberance: Animal Homosexuality and Natural Diversity.

Bagemihl's research shows that homosexual behavior, not necessarily sex, has been documented in about five hundred species as of 1999, ranging from primates to gut worms.

[41] Hypotheses contrived in an attempt to explain the behaviour – homosexuality in birds – typically diverge from one another, further exacerbating an apparent perception in the concerned scientific communities knowledge's quest to realise bird homosexuality remains elusive as an objective.

Research has shown that simulated mating behavior increases fertility for Aspidoscelis neomexicanus.

One female lies on top of another, playing the role of the male, the lizard that was on bottom has larger eggs, in most cases.

Roy and Silo , two Central Park Zoo male chinstrap penguins similar to those pictured, became internationally known when they successfully hatched and cared for an egg they were given. [ 1 ]
Couple of male mallard ducks in a nature reserve in Germany
Arctic grayling ( Thymallus arcticus ) leaping for a fly fisherman's bait. Research going back to the 1950s has shown both male and female graylings exhibit homosexual behavior. [ 53 ]
Three species of Aspidoscelis
The head of a darner dragonfly ( Basiaeschna janata )
Male flour beetles engage in same-sex coupling to practice mating and to rid themselves of "old, less effective" sperm .